Figure 1. Study design.

We considered 163 patients underwent to laparoscopic three-dimensional (3D) HD surgery. This prospective 3D-group was compared with a retrospective-prospective control 2D-group of patients who underwent the same surgical procedures between January 2010 and April 2017. The patients were selected at ratio 1:1, for every patient in 3D-group, a patient with the same characteristics and pathology was selected from 2D-group. We used random selection for patients. In the learning curve period from November 2012 to January 2013 we performed intensive basic laparoscopy (cholecystectomies and appendectomies) in order to familiarize with 3D system.